Aqua and Terra Orbits

Aqua's early afternoon observation time complements the 10:30-10:45 a.m. equatorial crossing time (descending in this case) of the EOS Terra satellite, launched in December 1999. The two daytime crossing times account for why the Terra and Aqua satellites were originally named "EOS AM" and "EOS PM", respectively. The combination of morning and afternoon observations allows studies concerning the diurnal variability of many Earth system parameters.